1. Field of the Invention
The present invention is related to a coal treatment process for a coal fired power plant, and particularly for a process, which is implemented with a coal-beneficiation process module to extract water, non-combustible ash, mercury and oil that are associated with coal before firing the coal.
2. Description of the Prior Art
Technologies for the treatment of coal to improve its quality as a fuel for power plants have been known including pyrolysis of coal with microwave energies. The following nine patents and published patent applications are the closest prior art references which are related to the present invention.    1. U.S. Pat. No. 3,449,213 issued to Edward M. Knapp et. al on Jun. 10, 1969 for “Pyrolysis of Coal With Microwave” (hereafter the “Knapp '213 Patent”);    2. U.S. Pat. No. 3,560,347 issued to Edward M. Knapp et. al on Feb. 2, 1971 for “Apparatus For Carbonizing Carbonaceous Materials Using Microwave Energy” (hereafter the “Knapp '347 Patent”);    3. U.S. Pat. No. 4,118,282 issued to Floyd D. Wallace and assigned to Wallace Energy Conversion, Inc. on Oct. 3, 1978 for “Process And Apparatus For The Destructive Distillation Of High Molecular Weight Organic Materials” (hereafter the “Wallace Patent”);    4. U.S. Pat. No. 4,123,230 issued to Chalmer G. Kirkbride on Oct. 31, 1978 for “Sulfur Removal From Coal” (hereafter the “Kirkbride '230 Patent”);    5. U.S. Pat. No. 4,148,614 issued to Chalmer G. Kirkbride on Apr. 10, 1979 for “Process For Removing Sulfur From Coal” (hereafter the “Kirkbride '614 Patent”);    6. U.S. Pat. No. 4,234,402 issued to Chalmer G. Kirkbride on Nov. 18, 1980 for “Sulfur Removal From Crude Petroleum” (hereafter the “Kirkbride '402 Patent”);    7. United States Patent Published Application No. US2007/0131591 to Frank G. Pringle and published on Jun. 14, 2007 for “Microwave-Based Recovery of Hydrocarbons and Fossil Fuels” (hereafter the “Pringle Patent Application”);    8. U.S. Pat. No. 4,259,560 issued to George W. Rhodes on Mar. 31, 1981 for “Process for Drying Coal and Other Conductive Materials Using Microwaves” (hereafter the “Rhodes Patent”); and    9. Australia Patent Published Application No WO/2007/028208 to Edek Choros and published on Mar. 15, 2007 for “Hybrid Energy System” (hereinafter the Choros patent application)
The Knapp '213 Patent discloses a method for recovering sophisticated volatile materials of commerce extracted by heat from coal. The method consists of the following four steps: (1) The heating of coal to a temperature of approximately 600 F; (2) The pyrolysis of the coal by the use of an industrial heating microwave unit to a temperature of approximately 800 F in a partial vacuum; (3) The total absorption of the effluent from the pyrolysis in an oil bath, followed by partial desorption of the chemicals of commerce at a temperature which separates the chemicals of commerce and (4) The vapor phase fractionation of the resulting gas stream prior to any commingling of the chemicals of commerce and before returning to ambient temperature.
The Knapp '347 Patent, which is a division of the Knapp '213 Patent, discloses an apparatus for carbonizing coal. The coal is first preheated in a first chamber by direct contact with hot gases, and is then carbonized in a second chamber using microwave energy as the heat source. The volatile materials from the second chamber are fractionally condensed.
The Wallace Patent discloses a process and apparatus for destructive distillation of high molecular weight organic materials such as organic wastes using ultrasonic and microwave generators together to irradiate and molecularly disperse the organic'molecules in the organic materials. Application of the patented technology produces products of clean gaseous volatile chemicals having a high fuel value and by-products of charcoal, tars, resins and pure carbon.
The Kirkbride '230 Patent discloses a process for decreasing the sulfur content of coal, including drying coal and subjecting the dried coal in a hydrogen atmosphere to the influence of microwave energy.
The Kirkbride '614 Patent discloses a process for decreasing the sulfur content of coal, including forming a slurry of coal particles in an inert solvent, and subjecting the slurry in admixture with hydrogen with microwave energy.
The Kirkbride '402 Patent discloses a process for decreasing the sulfur content of coal or crude petroleum, including drying coal and subjecting the dried coal in a hydrogen atmosphere to microwave energy.
The Pringle Patent Application discloses methods for decomposing and extracting compositions for the recovery of petroleum based materials from composites comprising those petroleum-based materials. The methods include subjecting the compositions and/or composites to microwave radiation in the range of from about 4 GHz to about 18 GHz.
The Rhodes Patent discloses a process for drying a conductive material, particularly coal, by subjecting the material to microwave energy, wherein a conductive aggregate is directed, through a region where microwave energy excites absorbed water molecules and the conductive material causes the water evaporate, resulting in a drier material.
The Choros Patent describes a hybrid method for producing energy from a carbonaceous material including the steps of: heating the carbonaceous material under a reduced oxygen atmosphere in a distillation plant to generate distillate vapors; processing the resulting distillate vapors; transferring the char residue from the distillation plant to a power station boiler; and combusting the char residue in the power station boiler for the generation of electrical power.
In general, coal is a primary energy resource to generate electricity at coal-fired power plants in numerous locations throughout the world. Coal is also associated with various other chemical substances, including water, non-combustible ash, mercury and oil. The presence of such chemicals causes significant problems in the coal firing process that is required for producing electricity. The coal's water content lowers the BTU energy value of the coal and reduces the power plant boiler's efficiency. The coal's non-combustible ash content results in boiler furnace erosion and ash-deposition problems. The coal's mercury content causes an air pollution emission, and the coal's oil values are lost during combustion, wasting a valuable natural resource of oil for transportation fuels.
The problems disclosed above have a significant impact on the environment, since a typical 500 mega watts (MW) coal-fired power plant consumes some 7,000 tons of coal a day. In the United States, Wyoming Powder River Basin coal (PRB) is frequently used because it has a low sulfur constituent. Typically, the PRB coal contains 15% to 25% of water, 6% to 15% of non-combustible ash, up to 40% of volatile matter (oil), and mercury constituents (approximately 100-150 parts per Billion). Therefore, if the 500 MW power plant uses the PRB coal every day, the equivalent of 260,000 gallons of water, 700 tons of non-combustible ash and 5,000 barrels of oil are estimated to be consumed, with about 1.4 pounds of mercury released to the atmosphere each day. In a situation where some 281 U.S. power plants fire PRB type coals, the collection and or control of such natural chemical substance in the coal is significant, both in economic impact and environmental protection to the United States. It also will be appreciated that the issue of such substance collection and or control is also critical to rest of the world, where coal fired power plants are frequently used.
A typical coal-fired power plant pulverizes the coal to a fine powder (approximately 50 micron in size) in a coal mill using hot “primary” air extracted from the power plant combustion air heater. As the coal is pulverized, the hot air evaporates the water in the coal and cools. The primary air then conveys the powdered coal along with the water vapor from the coal mill to the power plant coal burners, wherein the coal is burned to create heat and steam for electricity production. The water vapor from the coal that is carried along with the powdered coal into the furnace causes loss of heat energy and results in a boiler efficiency loss. A “rule of thumb” estimates that for each 10% of coal moisture carried into the furnace results in a 1% efficiency loss. Therefore, a method to remove the coal moisture from the furnace will improve the boiler efficiency.
Along with the coal, the non-combustible ash is also pulverized to a fine powder. This ash includes many natural elements and mineral compounds that may form air pollutants and or accumulate as mineral deposits on the boiler furnace surfaces. These deposits reduce the heat transfer from the hot combustion gases to the boiler surfaces, resulting in a reduced boiler efficiency. Additionally, some minerals may cause erosion and or corrosion of the boiler heat transfer surfaces. A reduction of the quantity of the ash passing through the furnace is needed to improve boiler operating reliability and efficiency.
Coal also contains traces of the element mercury. Recent air pollution regulations require stringent control of mercury emissions from power plants. The conventional mercury control methods capture the mercury from the exhaust gases downstream of the power plant where the mercury specie are very dilute (in parts per trillion) and difficult to capture. A method to efficiently remove the mercury from the coal before the coal is fired in the power plant is needed.
Many coals include a volatile hydrocarbon component that may be extracted as a crude oil product. Demonstrated thermal processes to extract oil from coal date from the 1850's, in England and Eastern U.S. driven by the need to avoid the extinction of Whales, a primary source of lamp oil for that period. More recent programs funded by the United States Department of Energy and others have further developed oil from coal extraction processes. The conventional oil extraction methods convey raw lumps of coal (two inch by two inch) to a sealed air-tight vessel. The coal lumps are carefully heated in the absence of air (pyrolyzed) to release some fraction of the volatile matter contained in the coal as an oil vapor. The oil vapor product is then transferred to an oil condenser and collected as a crude oil liquid. The crude oil must be further treated with hydrogen to make it suitable for conventional oil refinery processing into diesel, gasoline and jet fuels. Generally, the process to heat coal lumps is very slow with care to avoid over heating the coal, taking approximately 20 to 60 minutes to vaporize the oil. These time consuming methodologies of coal treatment result in significantly large and costly equipment installations in order process the many tons a day of coal required by a typical coal fired power plant and are not commercially viable.
Therefore, there is an important need to provide a method by which large quantities of coal can be processed very rapidly, right at the power plant site; to collect the water, non-combustible ash, mercury and oil values that are associated with the coal, thereby significantly improving the power plant electric generation efficiency with reduced pollutant emissions, and providing a reduced cost of operation through sale of the oil and water products.